1. Field of the Disclosure
The present disclosure relates to flow regimes in pipes. In particular, the present disclosure relates to sensor systems for detecting flow regimes in pipes.
2. Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
In power generation industries, such as the oil industry, flows in pipes and containers are carefully monitored, often with continuous online measurements of the flow patterns in pipe systems such as oil and gas pipelines, flow in boiler and reactor pipes; etc. In particular, local changes from single-phase flow to two-phase flow and flow pattern changes within two-phase flow are frequently monitored in areas such as pipe bends or in vertical segments of the pipe system where gravitational effects can modify the flow regime. A liquid in a two-phase flow is a mixture of two phases of a component, with different densities, at a certain ratio. This respective distribution or a ratio of a liquid to a vapor phase for example, is an important characteristic of two-phase flow. Similarly to the transition between laminar and turbulent flows in pipes, the transition between single-phase and two-phase flow, and flow regime changes can affect the performance of a pipe system. Accordingly, predicting the onset of two-phase flow or changes in the two-phase flow, i.e. changes in the ratio between the two fluids, are used to maximize system performance. Heat transfer models used in the industry to predict in-tube boiling and condensation are based on local flow patterns. Two-phase flow may develop during part of a steam cycle, wherein a mixture of gas and liquid may exist due to evaporation and condensation of steam. The ability to predict the occurrence of two-phase flow and to accurately determine its pattern is key to modeling phenomena such as evaporation and condensation. Accordingly, it is important to be able to accurately determine and model a transition from single-phase flow to a two-phase flow pattern, as well as transitions from one type of two-phase flow pattern to another.
Assessing whether a flow in a pipe system is a single phase flow or a two-phase flow is challenging. Depending on the nature of the flow, a different model may need to be used as an input, to provide an accurate heat transfer model for example. Furthermore, two-phase flow includes a variety of flow regimes, which require changes to a modeling scheme to obtain better accuracy in reproducing flow patterns.
Current techniques for measuring the two-phase flow include using Venturi pressure drop, Coriolis, electromagnetic, and cross-correlation flow meters, gamma-densitometry tomography, and electrical-impedance tomography. Empirical calibration is the prime methodology adopted by such techniques, while the detailed fluidelastic analysis has played a minimal role in instrument design and operation. Literature related to two-phase flow measurements also describes the use of time-of-flight pressure measurements, ultrasound wave trains, a flowmeter in a closed conduit, echoes of acoustic energy, speed of sound measurements and a Helmholtz resonator.
A phenomenon of cross-flow-induced vibrations is common to both the single-phase and two-phase flows. A cross-flow over a body induces fluidelastic coupling forces that cause a tube immersed in the flow to vibrate due to several fluid-structure interaction mechanisms; e.g. vortex shedding, fluidelastic whirling, turbulent buffeting, etc. For example, a cross-flow over a cylindrical body generates a Karman vortex sheet in the wake region of the body. Periodic shedding of these vortices from the surface of the body induces periodic pressure variations on the body which in turn give rise to flow-induced vibrations. Such vibrations frequently exist in direction both transverse and parallel to the cross-flow direction.
The characteristics of the cross-flow-induced vibrations are quite different for single-phase and two-phase flows due to different fluid-structure interactions. In two-phase flow, the presence of air bubbles give rise to random excitations of the cylinder; thus resulting in larger vibration amplitudes than in single-phase flows. Accordingly, the main difference between single-phase and two-phase flows is the variable buffeting force in the two-phase intermittent flow regime.